Thermostat



March 10, 1936. B. w. DEZOTELL THERMOSTAT Filed Aug. 7, 1954 Patented Mar. 10, 1936 UNITED STATES PATENT. OFFICE THERMOSTAT Application August 7, 1934, Serial No. 738,784 1 cam (or. 200-440) The present invention relates to thermostatically controlled devices employed in connection with electric circuits and the like, and is more particularly concerned with a thermostat for controlling the operation of an electric circuit designed for reception on the wall or similar appropriate place within a room the temperature of which is to be controlled.

This type of thermostat is commonly operated either by a bi-metallic member operating an electric switch, or a vapor filled bellows unit, which upon the creation of pressure causes similar operation of a switch. Both of these units have certain disadvantages which it is the purpose of the present invention to overcome. In addition, the invention is concerned with the design of a simple and compact form o2? which shall hold the temperature within close limits, and is capable long continued operation without additional regulation or setting.

in the accompanying drawing, Fig. i represents a side elevation oi a wail t ermostat embodying the features of the inven on; Fig. 2 is a front elevation of the same ture with the enclosing cover plate remove and Figs. 3 and i are front and side elevations, respectively, of the switch unit employed.

Referring particular the drawing, the in back plate it? having .med thereon, to which secured a sch-contained sv-Jitch unit it through mounting screws The switch unit comprises a housing portion it of insulating ma terial within which is e ed. aresilient swi blade 2dsecured a" car ying a contact 2 at its free end. The switch sled-e is actuated by pin 26 slidingiy mounted 3. housing and signed to engage the resilient blade in the region adjacent the anchor point. The blade is divided into three parts, which are arched or distorted with respect to one another in such a manner that pressure exerted by the pin 26 causes the curveture of the blade to reverse with a sudden and abrupt opening or closing movement of the switch.

The unit is electrically connected with appropriate lead-in wires through flexible connections and 32, connecting the terminals on the unit housing with corresponding terminals on the back plate of the instrument, as indicated in Fig. 2.

The operation of the unit is accomplished through a bellows thermostat 40 having a threaded stem 42 mounted in the projection 44 extending from a supporting plate 46 which is mounted upon the back plate. The bellows 'unit midway between its ends is provided with a. guide ring 48 which slides within a head 50 forming a part of the support 46 to maintain the bellows against distortion, and properly guide the free end with relation to the associated operating parts. The threaded stem 42 is connected to the adjacent- 5 end cf the bellows unit, and upon rotation bodily adjusts the unit in a lengthwise direction. The end of the bellows unit opposite the adjustment is provided with a stem 52 projecting through a guide member 54 formed on the support and serving to operate a lever 56 pivoted at 58 upon a tail 80 projecting from the support. The bellows is normally maintained in a. contracted pom'tion by a spring 52 inserted between the free end of the bellows and the support 54, and the lever 58 has capacity for adjustment with respect to the end of the operating stem through the provision of an adjusting screw 66 threadedly mounted in the depending end. of the lever and engaging the stem. The up er end of the lever is provided with an operating pin aligned. with the switch pin 2%, designed engage and move the switch pin for the purpose of opening the switch upon expansion of the bellows. Upon contraction of the bellows the svidtch itseh is self-restoring 2 to a closed position, and the lever 56 is caused to follow contraction of the bellows through. the spring "iii interposed between the lever and the wall of the switch housing.

An important and desirable adjunct of this 39 unit is due to the fact that the bellows theliilfistat is solidly filled with a iiquid, and expansion of the unit accordingly is created bv liquid expansion rather than by vapor pressure, the humid being such that no substantial vapor pressure is 35 created throughout the range of temperature at the instrument is used. By virtue of this fill, the movements of the bellows thermostat over any given temperature range are accurate and of equal increments for quick changes of temperature. Furthermore, the movement is positive, and the operation is accordingly not afiected by any variation in the force required to throw the switch. If the switch is capable of operation upon a predetermined and definite movement of the actuating element, the operation of the unit then becomes invariable as contrasted with a vapor filled bellows unit, which causes switch operation through the creation of pressure within the bellows unit rather than a predetermined and precise movement.

Because of the solidly filled character of th bellows thermostat with the positive movement created thereby on expansion of the liquid, I have found it desirable to interpose an over-running connection in the lever 56'to permit continued expansion of the bellows unit after the operation of the switch has been completed. To this end I slidingly mount the actuator pin 58 in theo'uter end of the lever 56, and normally maintain it in the position shown in Fig. 2 by a flat leaf spring 12 engaging; the end of the pin. Continued movement ofthe lever after opening of the switch with this construction is permitted byyielding movement of the holding spring 12.

The instrument is conveniently provided with a. temperature dial I4 mounted in a manner vto be visible through the housing, this dial turning with the adjustment of the unit through the threaded connection to indicate the temperature setting which is employed.

The initial adjustment for the purpose of calibrating the instrument is accomplished through the use of the set screw 66. Thereafter adjustmeans for adjustably anchoring the bellows at 10 one end, a lever connecting the free end of the bellows and the switch unit, adjustable connections between the'end of the lever and the bellows, meansior yieldingly retaining the bellows in contracted position, and independent means for' yield ingly retaining the lever in contact with the operating end of the bellows.

BERNARD W. DEZOTELL. 

